Agglomerating of loose materials into pillows or D-shaped lumps has been done by means of roll presses. These presses have rollers with pocketed surfaces to shape the material. Because of the high pressures, it is necessary to have some clearance between the rolls, but the briquettes are then formed with interconnected ligaments or lands of material between the individual pillows. This results in a briquette sheet which must be broken into its individual members. Especially when compacting iron ore or reduced iron ore, separation of the sheet with string breakers has been a problem; this is described in U.S. Pat. No. 3,593,378 and U.S. Pat. No. 3,300,815.
The briquettes from reduced iron ore are used in direct reduction processes. Commonly, iron ore is heated to about 1500.degree. to 1900.degree. F and formed into briquettes under roll pressures of 50 to 350 tons. In some cases, the iron ore is treated in a fluidized bed to remove about 5% of its oxygen, then it is briquetted for use in direct reduction processes; this is described in more detail in "The Making, Shaping and Treating of Steel", H.E. McGannon, ed, 9th ed, 1971, United States Steel Corporation, Pittsburgh, Pa., pp. 218-228, 403-421. In such processes, it is particularly important that the briquettes have smooth, complete shapes with a minimum of broken sizes and irregular jagged edges.